Introducing English Linguistics

saw similarities between the two kinds of parents 
(MICASE SGR565SU144)
?Similarities between the two kinds of parents were seen by us.
But despite the questionable acceptability of the above example, pas-
sivization is nevertheless a good indicator of a direct object.
Like direct objects, indirect objects can also undergo passivization.
However, indirect objects require a ditransitive verb: a verb that allows for
two objects. Each of the examples below contains a ditransitive verb followed
first by an indirect object (in italics) and then a direct object (in boldface):
She was showing